Looking for a DAC/Amp up to the $120 price range

I am going to be powering the HD598's most likely. At first I thought of getting the E10 but since I can fork over more money for the DAC/Amp what should I consider getting? Is there anything better than E10 at this price point?

If you can stretch till $149 I would suggest the Music Streamer II (MS II for short). I have the E10 and the MS II and while the E10 has a far more powerful amp that can drive even my orthos, the MS II is simply better in practically all aspects with soundstage being the most noticeable difference. The other differences are there but less noticeable unless you have a very revealing source and good quality music but the MS II has a very wide soundstage (among the best in its class) while the E10 has a rather narrow soundstage (practically worst in its class) so the difference is noticeable.

The E10 does have beautiful mids which I ever so slightly prefer over the MS 2. So if you listen to a lot of vocal oriented music the E10 might suit you better.

In addition to the MS II DAC you will need a 3.5mm female to RCA male connector as it doesn't have a headphone out. Don't worry the MS II is USB powered so it wont do any thing terrible to your headphones if you connect your HD598 directly to the MS II with the 3.5mm to RCA connector

^^ The MS II is a DAC and not a headphone amp. However for a relatively easy to drive headphone like the HD598 an amp isnt really required.

A powerful amp isn't needed, but current is. Especially since the HD598 is low impedance. The line out of the MS II is going to have low current. It's designed to be connected to a 100 kohm amp input. The impedance of line outs also have high output impedance (like 100 ohms), which is very bad with the HD598 in particular.